Steering Gear: Description and Operation

NOTE: The power rack and pinion steering gear is serviced as an assembly. If any service is required, the entire power rack and pinion steering gear must be replaced.

DESCRIPTION






The power rack and pinion steering gear is a hydraulic-mechanical unit which uses an integral piston and rack design to provide power-assisted vehicle steering control. The steering gear housing and valve housing are combined into a one-piece aluminum die casting.
^ The gear design incorporates quick connect fittings for the power steering left turn pressure hose and power steering return hose that allow the lines to swivel when detached from heat shield bracket. This is normal and does not indicate loose fittings.
^ If the fittings leak, check to make sure they are tightened to proper specifications. Do not over-tighten, as this may cause port seat damage.
^ If tightening the fittings to specification does not eliminate the leak, replace the fitting seals.

OPERATION






Internal valving directs pump flow and controls pressure, as required, to reduce steering effort during operation. The power rack and pinion steering gear contains a rotary hydraulic fluid control valve integrated to the power steering gear input shaft and control and a boost cylinder integrated with the steering gear rack.
Mechanical Operation
The power rack and pinion steering gear uses an integral piston and rack design to provide power-assisted vehicle steering control.
Hydraulic Operation






The power rack and pinion steering gear uses integral valving that directs pump flow and controls pressure as required to reduce steering effort during operation. The power rack and pinion steering gear contains:
^ a rotary hydraulic fluid control valve integrated to the power steering gear input shaft and control.
^ a boost cylinder integrated with the steering gear rack.
Rotary Valve
The rotary design control valve uses relative rotational motion of the power steering gear input shaft and control and valve sleeve to direct fluid flow.
^ When the steering wheel is turned, resistance of the wheels and the weight of the vehicle cause a torsion bar to deflect.
^ This deflection changes the position of the input shaft and sleeve ports, directing fluid under pressure to the appropriate end of the power cylinder.
^ The difference in pressure forces on the piston help move the steering gear rack to assist turning effort.
^ The piston is retained directly to the steering gear rack, and the steering gear housing functions as the power cylinder.
^ The fluid in the opposite end of the power cylinder is forced to the control valve and back to the pump reservoir.
^ When the driver stops applying steering effort, the valve is returned back to a centered position by the torsion bar.
^ When this occurs, pressure is equalized on both sides of the piston and the front wheels tend to return to a straight-ahead position.
VAPS
The rotary design control valve directs fluid flow using relative rotational motion of the power steering gear input shaft and control and valve sleeve. When the steering wheel is turned, resistance of the wheels and the weight of the vehicle causes a torsion bar to deflect.
^ The deflection changes the position of the valve spool and sleeve ports, directing pressurized fluid to the appropriate end of the power cylinder.
^ The difference in pressure forces on the piston helps move the steering gear sector shaft to assist turning effort.
^ The piston is attached directly to the steering gear sector shaft. The steering gear housing functions as the power cylinder.
^ The fluid in the opposite end of the power cylinder is forced to the control valve and back to the power steering fluid reservoir.
^ When the driver stops applying steering effort, the valve is returned back to a centered position by the torsion bar.
^ When this occurs, pressure is equalized on both sides of the piston and the front wheels tend to return to a straight-ahead position.